Hubble Rescue: Giving the Telescope Its Sight — an interactive Space Academy mission

When the Hubble Space Telescope reached orbit aboard Space Shuttle Discovery in April 1990, it was meant to be humanity's sharpest eye on the universe. Instead it sent home blurry, halo-ringed images. Engineers traced the flaw to the primary mirror: its outer edge had been ground too flat by about two microns — roughly one-fiftieth the width of a human hair — producing a defect called spherical aberration. The most expensive scientific instrument ever launched was, in effect, nearsighted, and the mistake became a very public embarrassment. But Hubble had been designed from the start to be serviced by astronauts, and NASA committed to the most ambitious repair mission the Space Shuttle program had ever attempted.

Space Shuttle Endeavour launched on STS-61 on December 2, 1993, carrying a seven-member crew and a payload bay full of new hardware. It climbed to an orbit of roughly 350 miles altitude to rendezvous with the free-flying, school-bus-sized telescope. Commander Dick Covey flew Endeavour to within a short distance of Hubble, and mission specialist Claude Nicollier used the shuttle's robotic arm to grapple the roughly eleven-ton observatory and berth it upright in the payload bay. Then came the heart of the mission: five spacewalks over as many days, an all-time record for a single flight at the time, worked by two alternating two-man teams that included veterans Story Musgrave and Kathryn Thornton. The astronauts replaced failing gyroscopes, installed two new solar arrays, swapped in the Wide Field and Planetary Camera 2 (which carried its own built-in optical correction), and installed COSTAR — the Corrective Optics Space Telescope Axial Replacement, a set of precisely positioned mirrors that acted as contact lenses for Hubble's other instruments. When one of the original European-built solar arrays was found bent and refused to roll up, the crew released it into space by hand so it would drift safely clear.

After the servicing was complete, Nicollier lifted Hubble back above the bay, and the arm released the telescope to fly on its own with a new set of eyes; Endeavour landed on December 13, 1993. The verdict came within weeks. On December 31, 1993, engineers aimed the new camera at the spiral galaxy M100, and the before-and-after images were transformative: the diffuse blur collapsed into pinpoint stars and a crisp galactic core. Hubble's trouble was over. The repair rescued not only a multibillion-dollar telescope but NASA's reputation, and it validated the entire concept of orbital servicing. Over the following decades and four more servicing missions, Hubble would go on to help measure the age of the universe, contribute to the discovery of dark energy, and deliver some of the most iconic images in the history of science — all made possible by the five-spacewalk marathon of STS-61.